Light beam switching and adjustment devices used for light path conversion are necessary in optical communications systems, and in recent years, matrix light beam switching and adjustment devices used to perform light path switching among a plurality of inputs and outputs have become especially important. For example, such matrix light beam switching and adjustment devices perform actions such as the transmission of light signals from one of numerous parallel input optical fibers to one of numerous parallel output optical fibers; a light beam switching and adjustment device such as that disclosed in Japanese Patent Application Kokai No. 2001-142008 is known as a concrete example of such a device.
In such a light beam switching and adjustment device, light from optical fibers is conducted to light guides in which light paths are formed in a matrix. Micromirrors using MEMS technology (MEMS: micro-electro-mechanical systems) are disposed at the intersection points of the light paths, and light path conversion and adjustment of the amount of transmission of the light beams are performed by moving these micro-mirrors into and out of slits disposed in the light paths.
FIG. 17 shows diagrams used to illustrate an example of the construction of a conventional light beam switching and adjustment device using MEMS technology. FIG. 17(a) is a plan view of this light beam switching and adjustment device, and FIG. 17(b) is a sectional view along line A–A′ in FIG. 17(a).
As is shown in FIG. 17(a), this light beam switching and adjustment device comprises first through third light guide cores 302a, 302b and 302c on a core supporting substrate 301. These light guide cores are connected to incident-side optical fibers 308 or transmission-side optical fibers 309, and slits 303 are disposed in the intersection parts of the light guide cores so that these slits cut across the light guides that intersect with each other.
Furthermore, an insertion plate supporting substrate 304 is disposed as shown in FIG. 17(b) on the upper surface region of the core supporting substrate 301 indicated by a dotted line in FIG. 17(a), and a structure is formed in which insertion plates 305 disposed on this insertion plate supporting substrate 304 are driven by an insertion plate driving mechanism 307. Furthermore, 306 indicates electrical wiring used for the electrical driving of the insertion plate driving mechanism.
The insertion plates 305 are disposed facing the upper portions of the slits 303. The insertion plates 305 are driven upward and downward by the insertion plate driving mechanism 307 so that these insertion plates 305 are inserted into or removed from the slits 303. As a result, a switching action based on the switching of the light paths of the light beams that enter the slits 303 from the optical fiber core parts 310 of the incident-side optical fibers 308, and an attenuation action based on the adjustment of the amount of transmitted light, can be accomplished.
Specifically, in a state in which the corresponding insertion plate 305 is inserted into the corresponding slit 303, the light beam that enters this slit 303 from the first light guide core 302a is reflected by the insertion plate 305, and is therefore coupled with the end surface of the second light guide core 302b. On the other hand, in a state in which this insertion plate 305 is withdrawn from the slit 303, the light beam that enters the slit 303 from the first light guide core 302a is coupled “as is” with the end surface of the facing third light guide core 302c. In this way, switching of the light paths of the light beams is performed, so that a switching action is realized.
Furthermore, if the insertion position (insertion depth) of the insertion plate 305 in the slit 303 is adjusted, an attenuation action that attenuates the intensity of the transmitted light can be realized by blocking a portion of the light beam that enters the slit 303 from the first light guide core 302a in accordance with this insertion position, and allowing the remaining light beam component to pass through so that this component is coupled with the end surface of the third light guide core 302c. 
In order to realize a light beam switching and adjustment device based on the system described above, it is necessary to attach MEMS actuators and micro-mirrors manufactured on the surface of a silicon substrate or the like by a MEMS process using a silicon semiconductor process or the like to a light guide substrate manufactured by a separate process. Specifically, in the manufacture of this light beam switching and adjustment device, it is necessary to join a light guide substrate which has mirror receiving recesses and an actuator substrate which has mirrors and actuators that support and move these mirrors, after aligning the mirrors and the mirror receiving recesses.
However, in the actual performance of such alignment, it has been ascertained that this alignment is extremely difficult. Specifically, since the mirror receiving recesses are disposed at intermediate points in the light guides, it is desirable that the width of the mirror receiving recesses be set as narrow as possible in order to suppress light loss. Accordingly, an extremely high degree of precision is required in the alignment of the mirrors and mirror receiving recesses. Furthermore, if the mirrors collide with parts other than the mirror receiving recesses in the process of this alignment of the mirrors relative to the mirror receiving recesses, the mirrors are easily damaged. Accordingly, the alignment of the light guide substrate and actuator substrate is extremely difficult. Especially in cases where the number of mirrors is large, all of the mirrors must be aligned with the corresponding mirror receiving recesses; accordingly, this alignment is extremely difficult.
Furthermore, the actuators are driven in accordance with signals. In the light beam switching and adjustment device of the present invention, the device has the following special characteristic: namely, the actuator substrate is joined with the light guide substrate in the assembly process. With this as a prerequisite, in order to reduce the size of the device and to facilitate inspections and the like during the manufacturing process, it is necessary to devise the structure of the wiring and the like that is used to supply signals to the actuator substrate so that this wiring, etc., does not interfere with the assembly, and so that inspections can easily be performed by connecting temporary wiring during such inspections.
Furthermore, in such a light beam switching and adjustment device, the relative positional relationship between the insertion plates and the slits formed in the light guide cores needs to be set so that the reflection loss is minimized when the insertion plates are caused to function as reflective plates. Furthermore, in order to reduce the loss of reflected light, it is desirable that the positions of the insertion plates with respect to the slits be aligned with a precision of 1 μm or better. Moreover, in cases where the amount of attenuation of the light beams is adjusted, the insertion plates must be smoothly driven by the insertion plate driving mechanism.
In order to observe the state of high-precision alignment of the insertion plates and slits in such a light beam adjustment device, it is important to accurately monitor these relative positions and the insertion depth of the insertion plates inside the slits from the outside.
Generally, a method is used in which microscopic observation by an optical method is used to monitor the relative positional relationship between the insertion plates and the slits following the bonding of the core supporting substrate and insertion plate supporting substrate, with observation being performed using an infrared microscope in cases where the device is constructed using silicon substrates, and using a common optical microscope equipped with a visible-light light source in cases where glass substrates are used.
However, in addition to the insertion plate driving mechanism being attached to the insertion plate supporting substrate, wiring used to operate the insertion plate driving mechanism is also disposed. Accordingly, the following problem arises: namely, the presence of such constituent elements is a major obstacle to observation of the relative positional relationship between the insertion plates and the slits.
Furthermore, the following problem is also encountered: specifically, the observational magnification during microscopic observation inevitably increases according to the width of the slits and the size of the insertion plates that are the objects of observation; accordingly, the depth of field is shallow, so that it is difficult to discriminate the insertion positions of the insertion plates inside the slits.